1. Field of the Invention
This invention relates to a vector quantizer and a vector quantization method, and more particularly to a vector quantizer and a vector quantization method that permit watermark information to be embedded in a coded bit stream in encoding a digital signal such as an audio signal or an image signal.
2. Prior Art
A vector quantizer which permits watermark information to be embedded in a digital code stream consisting of vector quantized indexes in accordance with embedding position designating information, for example, in a designated bit of a 5-bit index, has been proposed (Japanese Laid-Open Patent Publication No. 10-224342). The proposed vector quantizer is constructed such that it selects a quantization vector that has the least distortion with respect to an input vector from among indexes fixed in this manner, and outputs the index representing the selected quantization vector.
The proposed vector quantizer, however, has a drawback that since the embedding position is fixed, the position where the watermark information has been embedded can be identified using difference data obtained by comparing data that is obtained when encoding is performed with the watermark information embedded, with data that is obtained when encoding is performed with no watermark information embedded, for the same input signal string of finite length.
The proposed vector quantizer has another drawback that since the embedding position is determined without taking into consideration the effect on the quality of the reproduced signal, the influence of the embedded watermark information is exerted upon the entire reproduced signal, so that depending on the embedding position of the watermark information, a user may readily recognize degradation of the reproduced signal due to the addition of watermark information.